In order to assure a hermetic bond between the spacer frame and the glass sheets a mastic-like sealant material has been applied to opposite sides of the spacer frame continuously about the panel. A typical sealant material, such as polyisobutylene or a Butyl "hot melt" adhesive, is applied to the spacer frame, the spacer frame assembly is sandwiched between the glass sheets, and the panel is subjected to high energy radiant heating while the glass sheets are pressed against the spacer frame assembly. The sealant is heated sufficiently to "melt" and flow into sealing and bonding contact between the glass and the spacer frame. Upon cooling, and in use, the sealant material is relatively rigid although it does tend to exhibit plastic flow characteristics under stress.
In use the insulating glass panels are subjected to appreciable temperature differentials and to frequent temperature "cycling." The spacer frames therefore have been subjected to stresses and strain resulting from temperature induced differential expansion and contraction. In panels where the spacer frame segments were not firmly secured together, the applied stresses sometimes resulted in the frame segments shifting apart and causing the sealant material to deform sufficiently to break the seal between the frame and the glass. While the structural integrity of the panels was not usually adversely affected, the broken seals permitted a migration of atmospheric moisture into the dead air space.
Accordingly the use of corner connectors between spacer frame segments for securing the segments together and rigidifying the corners was proposed. The corner connectors were usually formed of relatively rigid plastic or zinc alloy materials and when attached to the frame segments provided sufficient strength to maintain the integrity of the spacer frame assembly.
Even though insulating glass panel components were hermetically bonded together and the seal remained intact, atmospheric moisture was trapped in the air space when the panels were being assembled. The trapped airborne moisture often condensed within the panels. In order to avoid this problem the prior art proposed the use of tubular spacer frame segments containing particulate desiccant material. The spacer frame segments were constructed from aluminum or galvanized sheet steel and formed with slightly open interiorly facing seams which permitted the segments to "breathe," i.e., the seams enabled communication between the desiccant material and the panel air space while preventing loss of desiccant into the air space. The desiccant material was effective to dehumidify the air trapped in the panel air space.
The construction of the spacer frames and panels was complicated by the use of desiccant materials in the frame segments. In order to prevent dumping the desiccant material out of the frame segments the frame segments were filled with desiccant material and assembled together using corner connectors which both plugged the ends of the frame segments and formed the spacer frame corners. The plugging action of the corner connectors in the frame segment ends did not produce a gas tight seal at the ends of the frame segments, but was effective to prevent loss of the desiccant while handling during manufacture of the panels.
Applying the sealant material to the spacer frame was accomplished by moving one side of the spacer frame past two or more sealant extrusion nozzles at a controlled rate of travel and repeating the process for each side of the polygonal spacer frame.
The spacer frame assembly thus formed had a doubled layer of the sealant at each corner of the frame. These layers had to be manually smoothed out and feathered into the single sealant layers adjacent the frame corners to assure that an effective seal could be provided with the glass sheets.
This assembly process was most effectively performed by using two sealant extrusion machines with an operator for each machine being responsible for applying the sealant to the frames. The frame assemblies from each extrusion machine were then placed on a respective table where a finishing operator smoothed the sealant at the corners. An inspector was usually present to inspect the frame assemblies after the finishing operators had completed their ministrations.
Even though excess sealant was present at the frame corners there was not usually enough sealant to permit complete encapsulation of the exterior of the corner connector by sealant material. In fact, complete encapsulation of the corner connector was necessary to prevent leakage into or from the panels along paths extending between the corner connector and the spacer frame segment ends, to the spacer frame and then to the space between the glass panels in the internal openings in the spacer frame segments.
Accordingly a layer of sealant was sometimes applied around the external corners of the spacer frames during the frame finishing operation. This required use of a separate specialized sealant extrusion nozzle and supply arrangement and materially slowed the finishing operation.
Assembly of the panels was then completed in the manner described previously. In some manufacturing operations, the panels were constructed without first applying sealant to the external corners, but after the panel was constructed the entire external periphery of the assembly was coated with sealant. This step required an operator, frame handling equipment, and a specialized sealant applying apparatus.
The spacer frame assembly process was relatively slow because of the multiple step sealant applying procedure. The extrusion machine had to be started and stopped repeatedly during the application of sealant to a single spacer frame and the sealant was usually applied at a relatively low application rate. Furthermore, application of the coatings was often difficult and cumbersome for the extrusion machine operator, particularly when large size frames had to be coated. For example, when spacer frames for sliding glass door panels were coated, the frames themselves were sometimes six feet long, or longer, per side and although the frame segments were securely connected together, the frames were still quite flexible and thus extremely difficult for the operator to manipulate. Application of the frame corner sealant materials, as noted, was inconvenient and required specialized equipment.
The assembly process was labor intensive and therefore costly since as many as five persons were required to produce spacer frame assemblies preparatory to forwarding them to the insulating glass panel production equipment. It should be noted that spacer frames cannot effectively be produced and stockpiled for eventual use without risking loss of effectiveness of the desiccant material in the frame segments before final assembly of the panels.